Construction for electric heaters for flexing bars



M. IRELAND March 18, 1952 CONSTRUCTION FOR ELECTRIC HEATERS FOR FLEXING BARS Filed July 19, 1946 TIE //V$ULA7/0/V INVENTOR.

Patented Mar. 18, 1952 CONSTRUCTION FOR ELECTRIC HEATERS FOR FLEXING BARS Murray Ireland, Elgin, Ill., assignor to McGraw Electric Company, Elgin, 111., a corporation of Delaware Application July 19, 1946, Serial No. 684,881

8 Claims.

My invention relates to electrically heated thermostats and particularly to the mounting of the electric heater thereof.

One object of my invention is to provide an electrical heating unit for a bimetal thermostat that shall not interfere with the free flexing of the bimetal bar.

Another object of my invention is to provide an electrical heating unit for a bimetal thermostatic bar that shall be loosely mounted on said bar.

Another object of my invention is to provide an electric heating unit for a bimetal thermostatic bar that shall be loosely supported on said bimetal bar and prevented from moving along said bar.

Another object of my invention is to provide an electric heating unit for a bimetal thermostatic bar that shall be easily and quickly manufactured and assembled and securely mounted in proper operative position thereon.

Other objects of my invention will either be apparent from a description of one form of device embodying my invention or will be pointed out in the course of such description and set forth more particularly in appended claims.

In the drawing,

Figure 1 is a top plan view of a thermostatic bimetal embodyin my invention,

Fig. 2 is a view in side elevation of the device shown in Fig. 1,

Fig. 3 is a sectional view therethrough taken on the line 33 of Fig. 2,

Fig. 4 is a fragmentary sectional view taken on the line 44 of Fig. 2 showing the relative positions of the bimetal bar and the heater element when the bimetal bar is flexed.

Fig. 5 is a perspective view of the heater element ready for assembly on the bimetal bar of Fig. 6, and,

Fig. 6 is a perspective view of the mounted end portion of a bimetal bar on which the heater element shown in Fig. 5 is placed.

i-leretofore when it was desired to heat a bimetal bar so as to cause it to flex, by means of a small heating element, the resistor conductor of the heater was wrapped tightly around a plurality of thin electric-insulating sheets, such as mica, which prevented engagement of the conductor and the bimetal bar. This has several obvious disadvantages, among them being that particularly when one end of a bimetal bar is fixedly supported and when the bimetal bar flexes, that there will be an undue amount of friction between the mica and the outside surface of the bimetal bar, which friction will also vary with the degree of pressure exerted by the assembler when winding the resistor conductor around the sheets of electric insulation as Well as the bimetal bar.

Referring now to Figs. 1 and 2 of the drawing, I have there illustrated a base H which may be made of any suitable or desired electric-insulating material which will withstand temperatures to which the bimetal bar as Well as the heating element will be heated. Upon one face of plate II, I provide a fixed support l3 of metal and of substantially L-shape, which is secured against the face of plate I l as by a machine screw IS. A bimetal bar I! of any suitable or desired length, thickness and width is secured to the vertically extending arm [9 of bracket [3 as by a pair of rivets 2|. The free end of bimetal bar I! may be provided with an adjustable contact surew 23 which is adapted to be engaged with and disengaged from a fixed contact 25 which is also supported on the same side or face of plate or block I l as is the bracket l 3. It is evident that the position of the specific bimetal bar ll shown in Fig. l of the drawing is that which it will occupy at say, ordinary room temperature and that it will flex in a counter-clockwise direction upon increase of temperature.

I provide a pair of relatively small sheets 2! and 29 of mica, being adapted to be positioned adjacent to, but spaced from, each side of the bimetal bar IT by means to be hereinafter described.

. Each of the sheets 21 and 29 of mica is provided with a plurality of recesses 3| in two opposed side edges, which side edges are adapted to be maintained parallel to the sides of bar 11.

I provide in addition a second sheet of mica 33 which is adapted to be positioned closely adjacent to say, sheet 29 for a purpose to be hereinafter set forth in detail. Sheet 33 is provided with substantially the same recesses 3| as are provided in plates 2! and 29.

A resistor strip 35 of a suitable width and thickness as well as length is adapted to be wrapped around sheet 21 as well as sheets 29 and 33 after the resistance conductor 35 has had connected to its ends leads 3! and 39 so that the strip 35 may be connected to terminal members 4| and 43 mounted on base I I. Since it is desired to make a good connection between the ends of strip 35 and the leads 31 and 39, the connection is made by soldering as well as by using a rivet 45 substantially as shown in Fig. 3 of the drawing. I may employ any suitable solder that has a melting point above the temperature to which the connection will be exposed during use of the device. This rivet 45 will therefore receive a head,

which head will be on the inner or the inside surface of plate 33 of mica, so that it is necessary to provide a second sheet of mica 29 to cover over the heads of rivets 45 to prevent their engaging the bimetal bar I! and thereby cause short-circuiting of the heater resistor 35.

I provide tubular spacers 41 and 49 for the mica-sheets, the length of which spacers is greater than the thickness of the bimetal bar [1. Furthermore, in order to permit flexing of the bimetal strip, as for example to permit it to flex to substantially the curvature of the bimetal strip shown in Fig. 4 of the drawing, I make the spacers 41 and 59 long enough that the mica strips 21, 29 and 33 will not tightly engage the bimetal strip.

Since it is desired to hold the heater comprising the resistor strip in its proper operative position which, in this case, is close to the mounted end, I provide a pair of elongated openings 5| and 53 in bar l1, opening 53 being slightly longer than opening 5|, opening 5! being adjacent one side edge of bar I! and opening 53 being adjacent to the other side edge of bar I1. I provide rivets 55 and 5'! which extend through not only the tubular spacer members but also through openings in the three strips of mica, which openings are just large enough to receive the rivets, as well as the bimetal bar I1, and these rivets will ensure the maintenance of the proper operative position of the heater on the bimetal bar I1.

In order to ensure that the initial distance between plates or strips 27 and 29 of mica will be maintained, I bend the resistance conductor 35 inwardly between the mica plates 21 and 29 as shown more particularly in Fig. 5 of the drawings by numeral 59. This inward bend holds the three sheets of mica, one on one side of the strip and the other two on the other side of the strip, in their proper operative spaced position substantially as shown in Fig. 4 of the drawing. It will be noted that openings 5! and 53 extend through opposite side edges of bimetal bar I! and that these openings extend through opposite ends of the sheets 21, 29 and 33 of mica.

The weight of a heater of this kind is relatively small so that with proper care in the positioning of openings 5| and 53 in bimetal bar I! the friction between the spacers 41 and 49 and the walls of openings 5| and 53, will be relatively very small, and I have found that the operation of a flexing bimetal bar of this kind is very positive and that there is little if any variation from a desired average when the individual bars are subjected to substantially the same temperature change.

I may here point out that I prefer to reduce the width of bimetal bar I! within the heater-unit hereinbefore described as by providing an elongated recess 6| on one side .of the bimetal bar and an elongated recess 63 on the other side of the bar, these recesses being slightly staggered along the length of bimetal bar I! so that the distance between the bent-in portions 59 of resistance strip 35 and the bimetal bar I1 will be a safe one which will not permit a break-down when the heating element is energized.

It is, of course, obvious that the heating element may be connected in series circuit with the bimetal bar or that it may be connected in an entirely separate energizing circuit and that it is not necessary that the bimetal bar carry current since it may be used to do mechanical work by flexing.

Various modifications may be made in the device set forth in my invention without departing 4 from the spirit and scope thereof and all such modifications'clearly coming within the scope of the appended claims shall be considered as part of my invention.

I claim as my invention:

1. The combination with a flexible bar, of a heater for heating said bar comprising sheets of electric insulation on opposite' sides of said bar, an electric-resistor strip wound around said sheets and encircling said bar and spacers fastened to said sheets and spacing them apart a distance greater than the thickness of said bar, said spacers being supported loosely by said bar so as to support the heater on said bar but permit limited movement of said bar with respect to the spacers and heater when said bar flexes.

2. The combination with a flexible bar, of an electric heating device for heating said bar, at least a part of said heating device lying along side said bar in spaced relation to said bar and opposing a substantial portion of the length of said bar, and fastener elements fastening said heating device to said bar and supporting it thereon in spaced relation, each fastener having connections with both said heating device and said bar and the connection with one thereof being loose so as to permit limited movement of said bar with respect to said heating device when the bar flexes.

3. The combination with a flexible bar, of an electric heating element encircling said bar, in spaced relation to said bar, a rigid supporting structure of electric insulation for the heating element having opposing portions on opposite sides of said bar and spaced farther apart than the thickness of said bar and spaced-apart fasener elements supporting said supportin structure on said bar, said fastener elements extending transversely through said bar and said supporting structure and having loose connections with one of them so as to permit limited movement of said bar with respect to the heating element and said supporting structure when said bar flexes.

4. The combination with a flexible bar, of an electric heater for heating said bar comprising a pair of thin sheets of electric insulation on opposite sides of said bar, a pair of spacers connecting said sheets and spacing them apart a distance greater than the thickness of said bar. said spacers extending through openings in said bar for supporting said heater thereon, said openings being large enough that said spacers are loose therein, and an electric resistance conductor supported on said sheets.

5. The combination of claim 4 wherein said sheets are wider than said bar and have notched edges, and said conductor is in the form of a ribbon wound about said sheets in said notches and bent inward in the space between said sheets to better secure it thereon.

6. The combination of claim 4 wherein said bar consists of thermally responsive bimetal and said sheets are composed of mica.

'7. The combination of claim 4 wherein at least one of said openings in said bar is elongated in the longitudinal direction of said bar.

' 8. The combination with a flexible bimetal bar of an electric heating element for heating said bar, said heating element having a part alongside said bar and opposing a substantial portion of the length of said bar in spaced relation to said .bar, a rigid supporting structure of electric insaid supporting structure to said bar and sup- 5 porting said rigid structure on said bar in spaced UNITED STATES PATENTS relation to said bar, each of said fastener elements Number Name Date having connections to both said rigid structure 926 714 Bradley June 29 1909 and said bar and the connection with one there- 1 5l7258 Smith 1924 by being loose so as to permit limited movement 5 2248531 Hams July 1941 of said bar with respect to said rigid structure 2'255169 Ireland Sept 1941 and said heating element when the bar flexes. 2:369:739 Johnson 1945 MURRAY IRELAND.

REFERENCES CITED 10 The following references are of record in the file of this patent: 

